1. Field of the Invention
The present invention relates to a multiplex transmission apparatus and a multiplex transmission method for ATM (Asynchronous Transfer Mode) communication.
2. Description of the Related Art
Conventionally, the traffic control method in the ATM network is conducted according to a service category of a VC (Virtual Channel) connection defined in an ATM layer. For example, as this service category, CBR (Constant Bit Rate), VBR (Variable Bit Rate), ABR (Available Bit Rate), UBR (Unspecified Bit Rate), and GFR (Guaranteed Bit Rate) are defined.
In the conventional traffic control method in the ATM network, a QoS (Quality of Service) condition requested by the user is satisfied by controlling traffic so as to satisfy the “QoS condition” of each service category. The service category of a VC connection is determined according to the traffic characteristic and the QoS request at the time of VC connection setting.
Typically, when transferring IP (Internet Protocol) packets, the ATM network transfers IP packets of a plurality of destinations on a single VC connection.
In the conventional traffic control method in the ATM network, however, a plurality of QoS conditions cannot be set in a single VC connection. When transferring IP packets having a plurality of QoS conditions set therein in the conventional ATM network, therefore, it is necessary to prepare as many VC connections as the number of QoS conditions set. In the conventional ATM network, therefore, there is a problem in that the number of VC connections increases and a limit is imposed on the ATM network construction condition.
In order to solve the problem, the following traffic control methods are known.
As a first traffic control method, there is known a method in which an ATM network uses a Diffserv (Differentiated Services) system, which is a QoS control technique in IP communication, when transferring IP packets having a plurality of QoS conditions set therein.
In the Diffserv system, the QoS condition of each IP packet is set in the IP packet header by “DSCP (Diffserv Code Point) information”. In the Diffserv system, processing on IP packets is conducted according to the DSCP every IP packet switching apparatus (router, switch, or the like). This processing of IP packets is called “PHB (Per Hop Behavior)”.
In the Diffserv system, PHB, such as EF (Expedited Forwarding), AF (Assured Forwarding), or Default, is defined by the DSCP.
As a second traffic control method, there is conceivable a method in which an ATM network uses an “AAL2 (ATM Adaptation Layer Type 2)” system in an upper layer above an ATM layer, when transferring IP packets having a plurality of QoS conditions set therein.
The AAL2 system aims at multiplexing a plurality of user connections on a single VC connection by using a frame that is shorter than an ATM cell of high efficiency coded audio information or the like.
As for an AAL2 connection used in the AAL2 system, it is possible to ensure a communication bandwidth with signaling. Furthermore, in the AAL2 system, it is possible to set a plurality of QoS conditions for each AAL2 connection. A technique of setting a plurality of Qos conditions in the AAL2 connection level is disclosed in Japanese Patent No. 3016400.
In the above described first traffic control method, however, a discard priority indication capability (three kinds can be set in AF PHB) in the Diffserv system is different from a discard priority indication capability (two kinds can be set by CLP (Cell Loss Priority)) in the ATM layer. This results in a problem in that it is necessary to convert the discard priority indication capability in the Diffserv system to the discard priority indication capability in the ATM layer, which is a lower indication capability.
Furthermore, in the AAL2 system, it is not supposed to conduct a traffic control that satisfies the QoS condition set in the IP network. Therefore, the above described second traffic control method has a problem that the traffic control and discard priority control using CLP per ATM cell can be conducted, but traffic control and discard priority control per CPS (Commonpart Sublayer) packet cannot be conducted.